Embodiments of the present invention relate to an optical film and, in particular, a polarization film.
In recent years, liquid crystal displays (LCDs) are experiencing a rapid development. More and more LCDs are putting into the market, and the application fields have been expanded. At the same time, there are still some problems on the display quality. Among these problems, the polarization film is one of the important factors causing the non-uniform luminance and the poor picture quality of the LCDs.
Currently, a polarization film generally comprises an adhesive layer (PSA), a light compensation layer (WVDL), a support layer (TAC), a polarization layer (PVA), a surface treatment layer, and the like. The fabricating process of the polarization film generally uses the processes such as pre-curing, laminating, coating, cutting, checking, packaging, and the like. The laminating process stretches the polarization layer in a predetermined laminating direction so that the iodine molecules within the layer are aligned along the laminating direction. When the light passes through the polarization layer (PVA), the iodine molecules absorb the light perpendicular to their alignment direction and allow the light parallel to their alignment direction to pass. In use, the polarization film is affixed onto the surface of a LCD panel, i.e., the adhesive layer (PSA) is affixed onto the surface of the color filter substrate and the array substrate of the LCD panel.
Since the laminating of the polarization layer (PVA) is a process in which exterior energy is compulsively applied to the layer in an original state, the polarization layer is in a state of absorbing energy, and there is a tendency for the polarization layer to return to the original state and release the energy at the conditions of high temperature and high humidity, i.e., there is a shrinkage force. Since the adhesive layer (PSA) is affixed onto the surface of the LCD panel, interaction force is generated between the polarization layer (PVA) and the adhesive layer (PSA). FIG. 5 is a schematic view showing the shrinkage state of the polarization film on the color filter substrate, FIG. 6 is a schematic view showing the shrinkage state of the polarization layer on the array substrate, and FIG. 7 is a schematic view showing the variation of light absorption axis caused by the shrinkage of the polarization film. As shown in FIGS. 5, 6 and 7, the polarization film shrinks as a whole in the condition of high temperature and high humidity, but it mainly shrinks along a direction opposite to the laminating direction under a restoring force. The shrinkage along the laminating direction is different from that along other directions other than the laminating direction, i.e., the polarization film on the color filter substrate mainly shrinks in direction A (FIG. 5), and the polarization film on the array substrate mainly shrinks in direction B (FIG. 6). Direction A and direction B are directions opposite to the laminating directions of the polarization film on the color filter substrate and on the array substrate, respectively. Normally, the light absorption axis of the polarization film on the color filter substrate and that of the polarization film on the array substrate are perpendicular to each other. However, due to shrinkage in direction A of the polarization film on the color filter substrate and shrinkage in direction B of the polarization film on the array substrate, the orthogonal relationship between the light absorption axes in the peripheral area of the two polarization films is changed (FIG. 7), so that the light leakage and the non-uniform luminance may arise in a black state, leading to the low quality of picture in a black state.